Exactly, especially with some types of batteries this is relevant. Redox flow batteries that are being experimented with for grid storage now use a reservoir fo

Exactly, especially with some types of batteries this is relevant. Redox flow batteries that are being experimented with for grid storage now use a reservoir for storing the anolyte and catolyte fluids. The bit that allows those to interface where the power is generated is much smaller though. So you can take the same battery and trivially double or triple the storage capacity by simply using bigger reservoirs and more liquid but the power delivery would stay the same. These types of battery are potentially great for longer term storage but they aren't necessarily able to deliver the stored energy quickly. It could take days/weeks to deplete them and a similar amount of time to charge them back up. Lithium ion grid batteries are sort of the opposite. They can deliver a lot of power but usually only for a few hours at maximum capacity until they are depleted. So, you see companies install a few hundred gwh of capacity being able to deliver most of that power in a few hours.